The present invention relates to a seatbelt retractor system for retracting the webbing of a seatbelt and, more particularly, it relates to a seatbelt retractor system having an energy absorption mechanism (an EA mechanism) for absorbing an inertial energy applied to an occupant when restraining the movement of the occupant by locking the seatbelt in an emergency to a seatbelt system.
Seatbelt systems provided to vehicle seats are essential systems for ensuring the safety of occupant's bodies by restraining abrupt movement of the occupants due to acceleration generated at vehicle collision.
The seatbelt systems generally include a webbing (belt), a retractor system, a buckle unit and the like.
The retractor system winds the webbing around a winder (a bobbin or a spool) to retract it inward by a spring force, and in a collision at which an impact is applied, locks the withdrawal of the webbing from the winder to thereby restrain the body of an occupant who is abruptly moving forward with the locked webbing. However, when the forward movement of the occupant is abruptly retrained, an impact by the reaction of the restraining is applied to the chest of the occupant and so on via the webbing. A method for energy absorption (hereinafter, referred to as “EA” as appropriate) has already been known to reduce the impact to the occupant. In a method disclosed by Japanese Patent No. 2875505, the collision energy applied to the occupant is absorbed in such a manner that a predetermined tensile load of the webbing is maintained while a larger withdrawing resistance than a fixed value is being applied to the webbing shortly after locking, and in this state, the webbing is withdrawn by a predetermined length.
The system of this conventional technique includes: a shaft disposed in a spool for winding the webbing in such a manner as to rotate relative to the spool; a locking mechanism that can lock the withdrawal of the webbing by stopping the rotation of the shaft; and a plastically deformable energy absorbing member (EA plate) disposed between the inner periphery of the spool and the outer periphery of the shaft. When the shaft is locked not to rotate by the locking mechanism in an emergency, the tension of the webbing that retrains the occupant who is moving forward by an inertial force acts as a turning force of the spool for winding the webbing relative to the shaft in the webbing withdrawing direction. When the relative turning force exceeds a fixed value, the EA plate is wound around the outer periphery of the shaft in the webbing withdrawing direction while being plastically deformed, thus absorbing the collision energy by the plastic deformation resistance, at that time. Accordingly, the spool rotates gradually whereas the locking mechanism is working, to withdraw the webbing while applying a fixed tension or more to the webbing, thereby reducing the force applied between the webbing and the occupant's body (see Japanese Patent No. 2875505 (Paragraph Nos. 53 to 60, FIGS. 7 and 8).
The above-described conventional technique, however, has the following problems.
In general, an impact at a collision depends on the structure of a vehicle. Accordingly, for sufficient protection of an occupant's body, it is necessary to optimize energy absorbing characteristics such as a set load (i.e., energy absorbing load; webbing tension at which absorption of energy is started) at which the energy absorbing mechanism starts operation and the amount of deformation when an impact is absorbed (i.e., webbing withdrawing stroke) and the like. As a result, flexibility and high design freedom for varying energy absorbing characteristics have been required for the entire retractor systems.
The foregoing conventional technique does not particularly consider changing of impact energy that the EA plate can absorb, and discloses no specific arrangement and principle of the changing. As a result, it was difficult to respond to the need for optimization of energy absorbing characteristics.
Since the EA plate has a specified width, the spool incorporating it increases in length, causing the obstruction to reduction of the size of the system.
Accordingly, it is an object of the invention to provide a seatbelt retractor system in which the energy absorbing characteristics can easily be optimized in response to the recent needs and which can be reduced in size, and a seatbelt system having the same.
Further objects and advantages of the invention will be apparent from the following description of the invention.